The Naiad Voyages

Mark Austen

2017.03.19 - Spar Shaping

Although the main task of today was the glueing up of the gaff, I wanted to shape the front end of the bowsprit to make sure that I could do it before I tried to shape anything else. The 'official" documentation about traditional boat spars indicates that the taper of a bowsprit should be 0.89 of the diameter at the stem. There is no official documentation as such but there have been a number of marine architects in bygone days that have written down the dimensions and ratios that they have used for their designs and 0.89 for a bowsprit seems to be about right. My bowsprit is 3" or 75mm in diameter at the stem which gives a figure of 2 2/3" or 67 mm at the end. I chose to make this 2" as Naiad is a small boat an therefore her dimensions can be less that the "quoted" figures which are for somewhat larger vessels. The bowsprit protrudes by 4' from the stem meaning that I have to cut a slope over the 48" that reduces the 3" square timber from nothing to 1/2" which is a very shallow angle. Much too shallow for me to even attempt to carry out by hand so I had to devise a jig.

The two glued up spars with the cramps, pads and plastic removed. You can easily see where the epoxy has squeezed out of the joins. On inspection there was one 2" section of the join on the boom where the epoxy had not squeezed out but you could see the epoxy in the join even so.

The ragged end of the bowsprit was cut off to give a square end. You can see that the timber has glued together very well. I like epoxy!

The square in the middle shows the size of the sprit once it has been shaped.

And that is the length of the taper. The pencilled line at 4' can just be seen at the lower part of the photo.

And here is the jig.

Two long straight pieces of wood have been clamped to the spar such that this end lines up with the marks on the end of the spar. The spacers are there so that I do not accidentally plane the guides.

At the 4' mark the guides are in line with the top of the spar as you can see by the rule resting on the spar.

I was all ready to start the shaping when I realised that using a power place at 09:00 on a Sunday morning would probably not be a very good thing to do if I wanted to stay on the good side of my neighbours, the sound of power planing wood carries quite some distance. So I took a coffee break.


So, after a coffee and some research on spar gauges, which you will understand later on in the spar building saga, I set to with power plane but carefully.

Care is needed since only the metal parts of the plane underside that should touch the guides but there is nothing to stop the plane from going too far over and planing the guides as well.

After 90 minutes of careful work here is the result. The nearest end is just 2" square and the farthest end is still 3" square.

You can see where the shaping ends as the epoxy is still on the surface of the wood.

So far, so good.

Now I need a rest since so much planing in one go make my back ache.

The gaff is now epoxied and clamped as you can see.

So the easy part of the spars has been done, now comes the harder part, that of the shaping. The tape of the bowsprit has been cut and the boom end also needs to be tapered but not over quite such a long length. All of the spars then need to be rounded.